Note: Descriptions are shown in the official language in which they were submitted.
CA 02431607 2003-06-10
ELECTROSTATIC FLOCKING AND ARTICLES MADE THEREFROM
Field of the Invention
The present invention relates to an elastic article with at least one
surface having densely populated orientated fibers and a process and
apparatus for the manufacture of the article. More particularly, the present
invention is directed to an electrostatically flocked glove and a process and
apparatus for making the flocked glove.
io Background of the Invention
The present method for applying flock to latex or latex/neoprene articles
involves coating the article with a thin layer of latex adhesive and
pheumatically blowing flock (most commonly chopped cotton) into the latex
adhesive layer while the adhesive is dried and cured. The curing results in
the
is cross-linking of the latex polymer molecules by sulfur bonds, or other
cross-
linking agents / mechanisms which provide memory to the polymer structure,
so when stretched it will rebound to its original cured shape. The cured latex
adhesive layer is imbedded with the flock. In the case of gloves, the glove is
inverted, thus flipping the flocked layer to the inside of the glove. Loose,
20 excess flock can then be removed from the article by washing and drying in
a
tumbler, chlorinating and drying in a tumbler, or just tumbling, depending on
the process. The flocked surface provides a slip layer for donning or removing
the glove and absorbing hand moisture.
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One major drawback with the present method is that it does not allow
the flock to be oriented, since the cotton flock is prepared by chopping and
crushing scrap cotton fabric, resulting in random cut lengths of various
shapes
and sizes. The chopped cotton is pneumatically applied, so the flock adheres
to the latex adhesive in whatever random orientation it first contacts the
adhesive surface. Thus, the cotton fiber may provide a slip coating for
donning and some moisture absorption but it does not provide a smooth, silky,
slippery, finished feel, as desired by a glove user.
Electrostatic application of flock to a non-uniform surface, such as a
rubber glove surface, can be problematic due to the convoluted surface.
When the article is a glove, the glove is typically rotated in an electrical
field in
order to present all surfaces to the electrostatic applicator. A typical
rubber
is glove manufacturing operation is a continuous conveyer system or conveyer
batch system where individual glove rotation may not possible. Therefore the
flocking operation must be designed to be a continuous system and designed
to keep up with manufacturing speeds. Moreover, the electrostatic flock that
has been spent through the charging nozzle or plate needs to be collected and
returned through the flock system for another opportunity at adhesion to the
adhesive layer on subsequent articles that are being continuously conveyed
through the flocking system.
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Presently, a known process used to apply an electrostatic flock layer to
a polyvinyl chloride polymer (PVC) glove includes the use of non-elastic
waterproof adhesives. Since a vinyl glove does not stretch in the typical
fashion of rubber articles, the complexity of a waterproof adhesive associated
with rubber articles is not experienced, as non-elastic waterproof adhesives
are readily available. High temperature cure adhesives are easily applied to
the PVC glove since the PVC requires temperatures exceeding 300 F. Thus,
the glove and adhesive temperature is matched. However, this technology
cannot be equally applied to rubber or rubber-based articles, such as gloves.
1o High temperature cure adhesives are incompatible with rubber-based gloves,
since rubber will typically begin to degrade at temperatures of 300 F and
above.
Therefore, there is a need in the art for an efficient process for forming
is a flocked rubber-based article, such as a glove. The present invention
provides for an efficient process that results in an electrostatically flocked
rubber-based glove with a smooth, silky feel, which is also very soft, elastic
and comfortably flexible. The present invention is achieved in part through
the
electrostatic application of precision cut, perpendicularly oriented fibers to
a
20 glove surface having an elastic adhesive system. Perpendicular orientation
and close packing of the electrostatic fibers also allows for much greater
moisture absorption to keep hands drier.
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Summary of the Invention
It is an object of the present invention to provide an article with at least
one surface coated with electrostatically flocked material.
It is another object of the present invention to provide such an article
that is an elastic article.
It is yet another object of the present invention to provide such an
elastic article with at least one surface coated with an electrostatically
oriented
io flock fiber.
It is a further object of the present invention to provide such an elastic
article with an elastic adhesive system for adhering the flock to the surface
of
the elastic article.
It is still a further object of the present invention to provide a process for
making an electrostatically flocked article.
It is yet a further object of the present invention to provide an apparatus
for making an electrostatically flocked article.
In brief summary, the present invention provides an article having at
least one surface coated with electrostatically flocked material. The flock
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material used is one or more fibers and preferably one or more synthetic,
precision length cut fibers. When electrostatically flocked onto the article
surface, the flock material is perpendicularly, or virtually perpendicularly,
oriented in an elastic adhesive, thus providing a silky smooth feel to the
surface of the elastic article. The present invention also provides a process
and apparatus for electrostatically flocking material onto an article.
In the Drawings
Fig. 1 is a plan view of a flocking apparatus according to the present
invention.
Detailed Description of the Invention
The present invention provides an article with at least one surface
having electrostatically flocked material. Preferably, the electrostatically
flocked material is coated to at least one surface. The material is oriented
on
the surface of the article, thus providing a soft, silky feel. Suitable
articles
include, but are not limited to, a glove, a medical wrap, a sport related
support
wrap for joints (i.e., wrist, knee, elbow and ankle), or other items such as
clothing, and any other item where a flocked surface is desired. In a
preferred
embodiment of the present invention, the article is a highly elastic article
such
as, for example, a rubber-based household glove.
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As used herein, a rubber-based article is one that may include, among
other constituents, natural rubber, synthetic rubber as defined in ASTM
D1566-98, or any combinations thereof.
The elastic article according to the present invention may be formed by
one or more layers of elastic material. When two or more layers of elastic
material are used, the elastic article may be referred to as a laminate or a
laminate structure. In forming a laminate structure, each layer of material
may
be of the same elastic material, or each layer could be of differing elastic
to materials. The final elastic article, regardless of its construction,
should meet
a Tensile Set of under 40% of the original elongation as tested by ASTM
D412-98, to which the elastic article is strained to no less than 80% of its
ultimate elongation. Preferably, the final elastic article, regardless of its
construction, should meet a Tensile Set of under 30% of the original
elongation as tested by ASTM D412-98, to which the elastic article is strained
to no less than 80% of its ultimate elongation. Most preferably, the final
elastic
article, regardless of its construction, should meet a Tensile Set of under
20%
of the original elongation as tested by ASTM D412-98, to which the elastic
article is strained to no less than 80% of its ultimate elongation.
Suitable flock material for use with the present invention includes, but is
not limited to, rayon, nylon, polyester, acrylic, or any combinations thereof.
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Preferably, the flock material is in fiber form and is precision cut. In a
preferred embodiment of the present invention, the fiber is precision cut
rayon.
To orient the fibers in a substantially perpendicular plane, the fiber used
is treated with a material or coating to provide each fiber with a negative
and
positive charged (polarized) end. Any suitable coating that polarizes a fiber
may be used in the present invention. Suitable polarizing coatings include
commercially available AC (Alternating Current) or DC (Direct Current) type
coatings, depending on the electrostatic flocking system selected.
It has been found that by controlling both the length of the fiber and the
denier of the fiber used in the electrostatic flocking process, optimization
of not
only the manufacturing efficiency, but also the feel and performance of the
elastic article is achieved.
The fibers used in the present invention have a length of about 0.005
inches to about 0.25 inches. Preferably, the fibers have a length of about
0.01
inches to about 0.03 inches, and more preferably about 0.012 inches to about
0.025 inches.
The fibers used in the present invention have a denier of about 0.9 to
about 7. More preferably, the fibers have a denier of about 1 to about 3, and
more preferably about 1.25 to about 2.
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To adhere the flock material to the surface of the elastic article of the
present invention, an elastic adhesive system is required and forms a critical
aspect of the invention. Since the elastic article of the present invention is
flexible, the adhesive used to adhere the flock to the article must also
possess
flexibility or elongation properties that are at least comparable to the
elastic
material used to form the article. Accordingly, through the use of such an
elastic adhesive, not only is the overall elasticity of the elastic article
maintained, the flock material embedded in the elastic adhesive does not
io separate from the adhesive. To achieve this result, the elastic adhesive
preferably includes any polymer capable of providing the adhesive with an
elongation of about 400% to about 1400% from its original state. More
preferably, the adhesive has an elongation of about 600% to about 900%.
When the article of the present invention is a rubber-based glove,
preferably, the adhesive system preferably includes a low temperature self
cross-linking water dispersed acrylic emulsion. This low temperature acrylic
adhesive system will cross-link at the same cure or cross-linking temperatures
required for a rubber-based glove, which is usually 230 to 250 F, over a time
range of 10 to 45 minutes depending on the product. Matching the cross-link
temperatures and oven time requirements between the acrylic adhesive
system and the rubber-based glove of the present invention is a critical
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manufacturing step. Acrylics that require at least 300 F to cross-link can
destroy the rubber-based portion of the glove or elastic article.
In addition, it has been found that the use of an acrylic adhesive system
of the present invention can impart a soft, smooth, and silky, as well as a
relaxed or cloth-like feel, to the body of the rubber-based glove. The unique
combination of the low-temperature adhesive system, the rubber-based glove,
and the electrostatic flock is critical to providing the soft, silky feel of
the glove
of the present invention.
Another critical element of the adhesive system of the present invention
is that the adhesive system holds the flock during wet service. To further
improve the high wet adhesion that is required for application to the glove of
the present invention, which may be used with water and surfactant solutions,
the adhesive may be adjusted to increase the wet bond. By way of example,
the wet bond may be adjusted by the inclusion, in the adhesive, of one or
more materials including, but limited to, resin compound, melamine-
formaldehyde resin, polychloroprene rubber, acrylonitrile rubber, styrene-
butadiene rubber, urethane or other synthetic rubbers, or any combinations
thereof. Preferably, the adhesive is compounded with a melamine-
formaldehyde resin to further waterproof the bond between the flock and the
adhesive.
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Also, a combination of two or more acrylics varying in durometer
hardness may also be blended together to modify the wet adhesion as may be
required for a product. Generally, the harder acrylics with less elongation
can
increase the wet adhesion. Also, when blended with the softer acrylics, the
harder acrylics can impart wet adhesion while not significantly compromising
the ease of elongation or flexibility of the elastic article. Therefore,
higher
concentrations of the harder acrylics lattices should increase bond strength.
Suitable acrylics for use in the adhesive system of the present invention
1o include, but are not limited to, a variety of commercially available
aqueous
acrylic copolymer emulsions. Copolymer types are selected depending on film
flexibility and time /temperatures required for cross-linking.
Suitable commercially available acrylic adhesives, include, but are not
limited to, Acrygen from Omnova, Nacrylic from National Starch, Hycar and
HyStretch from BF Goodrich, or any combinations thereof. Preferably, the
acrylic adhesive used is Acrygen , Nacrylic , or any combination thereof.
Suitable non-acrylic adhesives that can be used in the present
invention, depending on the product application, include, but are not limited
to,
any adhesive from polymers of natural latex, polychloroprene, acrylonitrile,
styrene-butadiene, urethanes, or any combinations thereof, combinations with
CA 02431607 2003-06-10
acrylics and melamine or other cross-linking resins and systems, or any
combinations thereof.
To further achieve the soft, silky feel of the flocked surface of the
rubber-based glove of the present invention, the flocked fibers are
electrostatically oriented on the surface of the glove in a perpendicular, or
virtually perpendicular, plane, meaning only one end of the straight, rod
shaped fiber is inserted into the adhesive. This orientation of the
electrostatically applied fibers in the adhesive also allows the adhesive to
1o stretch or flex with ease, as opposed to random oriented fibers, which will
bind
up the adhesive. The perpendicular orientation of the electrostatic flocked
fibers also allows for increased fiber packing or density over the surface of
the
adhesive to create a dense, smooth and level flocked surface. Therefore, the
orientated fibers provide both a very smooth and silky feel to the surface of
the
glove. Because only the ends of the fiber are in the adhesive, it allows the
adhesive to retain its elasticity and not to be bound up as random fiber
flocking
will do.
The present invention is also directed to a process for applying
electrostatically flocked fiber to the surface of a rubber-based article, such
as a
glove. The process involves the orientation and delivery of electrostatically
charged fibers into an adhesive layer applied to the surface of the glove. The
fibers receive their orientation and momentum through an electrical charge
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and travel to the electrically grounded adhesive surface thus planting one end
of
the fiber in a general perpendicular position to the surface.
Referring to Fig. 1, a preferred apparatus for electrostatically applying
flock to a
rubber-based glove is represented generally by reference numeral 10. The
apparatus
has a flock delivery and recovery system represented generally by reference
numeral
20, and a electrostatic flocking system represented generally by reference
numeral 50.
The flock feed system includes a flock storage hopper 22 from which the flock
metering system 24 feeds the proper portions of flock into the venture 26. The
electrostatic flock system 50 is generally operated by compressed or fan
driven air 28.
The air is driven through the venture 26, or other mixing chamber, which
propels the
flock and air mixture to the electrically charged nozzle 52.
The electrostatic flock system 50 has one or more oscillating electrostatic
flock
nozzles 52. Each nozzle is AC or DC charged, depending on the system, by a
power
supply 54. Once the flock leaves nozzles 52, it is orientated by the
electrical field, which
is generated between an electrode 56 on the flock nozzle 52 and the grounded
glove
former 58. A combination of electrostatic charge and slight pneumatic pressure
and
nozzle oscillations will distribute the flock over the convoluted surfaces of
a glove on
glove former 58. The glove formers 58 onto which the glove film and adhesive
has been
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applied in the previous manufacturing steps are moved through and past the
flock nozzles 52 via a continuous chain conveyer system (not shown), the
conveyer being part of the normal manufacturing process.
The excess flock 60 that does not adhere to a glove on glove former 58
is collected in flock collection unit 62. Excess flock 60 is sent by vacuum 64
to
a separator/ filter chamber 66, which expels clean air 68 through a filter 70.
Gravity drops the flock to collector 72, where it can be reloaded into the
feed
hopper 22.
Flocked gloves are then conveyed through an oven (not shown) for
drying and curing of the polymers to initiate the polymer cross-linking. At
the
end of the oven cycle, the glove is stripped from the former 58. The glove
will
undergo a separate washing and chlorination cycle (not shown) that is typical
is to glove manufacture. The washing and chlorination step will harden the
outside rubber surface of the glove to de-tack the rubber and render it smooth
or slippery to the touch.
While the apparatus depicted in Fig. 1 is described as operating
continuously, it should be understood that it could easily be adapted to
operate in the same fashion on a batch system basis.
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It should be understood that the foregoing description is only illustrative
of the present invention. Various alternatives and modifications can be
devised by those skilled in the art without departing from the invention.
Accordingly, the present invention is intended to embrace all such
alternatives,
modifications and variances.
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